Water from a domestic septic tank system contains organic matter (BOD), dissolved ammonium, etc, and needs to be aerated. Aeration oxidises the ammonium to nitrate, and cleanses the water of the BOD. Often, in conventional systems, a tile-bed soakaway, or the like, is provided, whereby the ammonium-containing (and BOD-containing) water is trickled onto and into the ground, where it is exposed to oxygen (from the atmosphere).
In that case, the function of aerating the water, and the function of infiltrating the water into the ground, are not separated, but are combined in the soakaway. The idea is that the water that passes down into the groundwater below the soakaway, having been through an aeration phase, in the soil, has had all its ammonium converted to nitrate, and its BOD into carbon dioxide and water, as the water passes into the aquifer.
The conventional tile-bed soakaway has not been satisfactory in some cases, usually because the water passing through the soakaway has not been aerated enough. In those cases, a separate water-aeration station may be utilised, in which the aerobic reactions can be completed, and can be seen to be completed, before the water is infiltrated into the ground. Such a separate water-aeration apparatus may be of the kind as disclosed in USA patent U.S. Pat. No. 5,762,784 (Jowett, June 1998).
When the water aeration treatment takes place in a separate aeration station, as in the above patent, the water then remains to be infiltrated into the ground. The invention is concerned with the system by means of which fully treated water may be infiltrated into the ground. The system of the invention may also be used with water that has been only partially pre-aerated, at a separate aeration station, and the final aeration takes place as the water is being infiltrated into the ground. The system of the invention may also be used with water that has not been pre-aerated at all, although that is less preferred.
The invention, preferably, is intended for use with treatment systems in which the water from the septic tank is subjected to the aerobic treatment before the water reaches the ground. Here, the aerobic reactions are enabled and promoted in e.g an above-ground aerobic facility. It is recognised that it is much easier to design the overall or whole system to operate efficiently, when the facility that handles the aerobic treatment chemistry is separate from the facility that handles the physical infiltration of the water into the ground. When the aeration-facility and the infiltration-facility are combined, as in the traditional tile-bed soakaway, the function of each is compromised by the need to accommodate the other.
The sagging-pipe infiltration system, as described herein, is aimed at addressing the above points. The sagging-pipe infiltration system may be used when the water entering the infiltration system is untreated, i.e when the water is effluent water straight from the septic tank. However, that manner of use is not preferred, because in that case some build-up of slimes and solids can occur, depending on such parameters as temperature, frequency of dosing, etc. The use of the infiltration system is preferred in cases where the water has been more or less completely aerated before being infiltrated into the ground.
On the other hand, it is preferred sometimes to use the sagging-pipe infiltration system in cases where only some of the aeration pre-treatment has taken place, for example when the aeration station is sized so as to cope with only the normal dosings of water. Then, any heavy dosings that might occur will result in some untreated water passing to the infiltration system. Under heavy dosing, the extra aerobic treatment would then have to take place on and in the ground, while the aerobic treatment of normal dosings would take place wholly in the aeration station.
In the sagging-pipe infiltration system, as described herein, the aim is that water can drain substantially completely from the pipe, along the whole length of the pipe, between dosings.
Another aim of the sagging-pipe infiltration system, as described herein, is that the water drains from the pipe evenly, along the length of the pipe. The water drains into a trench, or the like, underneath the pipe. As the designer of the system becomes confident that the water will be deposited very evenly in the trench, so the designer can take advantage of the resulting efficiency, to minimise the total size of the trench.
It is an aim of the invention to provide a system in which, during dosings, the pipe is completely filled with water, and pressurised, as a way of ensuring evenness of expulsion of water from the pipe, and in which water drains completely from the pipe between dosings.
A system in which the pipe did not drain completely would be unsatisfactory, because the residual water would freeze in cold weather, and at least partially block the pipe. In warm weather, water left in the pipe could become stagnant, leading to slime build-up between dosings.